Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.
FEC is a frequently employed sender-based technique to combat packet loss in packet-switched networks. Media-independent FEC, such as Reed-Solomon (RS) codes, produces n packets of data from k packets such that the original k packets can be exactly recovered by receiving any subset of k (or more) packets. On the other hand media-dependent FEC generates a redundant packet or payload that is often of lower bitrate (LBR) than Media independent FEC and consequently the recovered signal has lower quality than the original audio signal. LBR payload can be created using the same codec for the primary encoding when the codec supports the required low bitrate, or a completely different low bitrate codec (often with higher complexity).
It is evident that FEC improves voice quality at the expense of increasing bandwidth consumption and delay with redundant payloads, which can sometimes lead to unnecessary waste of precious network bandwidth, even worse, degraded performance due to network congestion. To address this issue, practical systems are often designed to be adaptive. For example, the system disclosed in the Bolot et al. adjusts FEC redundancy and coding rate dynamically according to the measured packet loss rate, which is estimated somewhere in the network and signalled back to the sender, e.g., through RTCP.
Empirically determining an optimal FEC scheme appropriate for the current network condition, bandwidth constraint, and audio codec can be time consuming. The aforementioned references propose methods to generate optimal FEC schemes based on an analytic model. However, several critical factors are missing from the model, which make the model less effective in practice.